光激發超極化氣體在低場磁振造影之特性研究

Low-Field Magnetic Resonance Imaging by Optical-Pumped Hyperpolarized Gas

熊良瑜(Liang-Yu Hsiung)

指導教授 ： 王立民

國立臺灣大學/理學院/物理學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201803158

摘要

本研究架設「光激發超極化氣體與低場核磁共振系統」，主要是經由數據擷取卡(DAQ)整合雷射系統、加熱系統和磁場等裝置，穩定的將3He或129Xe極化並測量核磁共振訊號。實驗經由電源供應器輸出穩定電流於主磁場線圈以產生穩定約10高斯的低磁場，並經由數據截取卡（DAQ）輸出所需要脈衝電壓、梯度電壓。並透過更換電容的方式，視所要量測的樣品調整系統共振頻率。經由數據擷取卡量測水(共振頻率為42800 Hz)、SF6氣體(共振頻率為42800 Hz)和光激發3He(共振頻率為32320 Hz)、129Xe(共振頻率為10400 Hz)氣體的核磁共振訊號頻譜。結合梯度補償的方式使得3He的核磁共振訊號的訊雜比從16提升到62、線寬從29 Hz降低到10 Hz，並利用gradient echo的方式成功地完成了光激發3He氣體的核磁共振造影。

關鍵字

光激發 ； 極化惰性氣體 ； 核磁共振 ； 低磁場核磁共振造影

並列摘要

In this study, we set up an "optical pumped hyperpolarized gas and low-field magnetic resonance imaging (MRI) system ", in which the laser systems, the heating systems and magnetic devices are integrated by the data acquisition card (DAQ) . Using this system, we polarize 3He and 129Xe stably and measure the magnetic resonance signals. The experiment outputs a steady current through the power supply, generates a stable low magnetic field (about 10 Gauss) via the coil. We use the DAQ to output the required pulse voltage and gradient voltage. By replacing the capacitor, the system resonance frequency (fr) can be adjusted according to optical-pumped gas or water measured. We measure the NMR signals of water (fr = 42800 Hz), SF6 gas (fr = 42800 Hz), hyperpolarized 3He (fr = 32320 Hz), and 129Xe gas (fr = 10400 Hz) by the DAQ. With the gradient compensation method, the signal-to-noise ratio of the 3He NMR signal is increased from 16 to 62, and the line width is reduced from 29 Hz to 10 Hz. Finally, we successfully use the gradient echo method to create the nuclear magnetic resonance image of the hyperpolarized 3He gas.

並列關鍵字

optical pumping ； hyperpolarized gas ； Nuclear Magnetic Resonance ； low-field magnetic resonance imaging

參考文獻

[1] M. A. Bouchiat, T. R. Carver, and C. M. Varnum, Nuclear Polarization in 3He Gas Induced by Optical Pumping and Dipolar Exchange, Phys. Rev. Lett. 5,373(1960).

[2] R.L. Gamblin and T. R. Carver, Polarization and Relaxation Processes in 3He Gas Phys. Rev. 138, A946 (1965).

[3] X. Zeng, E. Miron, W. A. van Wijngaarden, D. Schreiber, and W.Happer, Polarization of the nuclear spins of noble-gas atoms by spin exchange with optically pumped alkali-metal atoms, Phys. Lett. 96A,191 (1983).

[4] B. Chann, E. Babcock, L.W. Anderson, T.G. Walker, W.C. Chen, T.B.Smith, A.K. Thomson, and T.B. Gentile, Gas cells for 3He hyperpolarized via spin-exchange optical pumping, J. Appl. Phys. 94, 6908 (2003)

[5] T. G. Walker and W. Happer, Spin-Rotation Interaction of Noble-Gas Alkali-Metal Atom Pairs, Rev. Mod. Phys. 44, 169 (1972).